Enhanced Kerr Nonlinearity and Nonlinear Figure of Merit in Silicon Nanowires Integrated with 2D Graphene Oxide Films

Abstract

Layered two-dimensional (2D) graphene oxide (GO) films are integrated with silicon-on-insulator (SOI) nanowire waveguides to experimentally demonstrate an enhanced Kerr nonlinearity, observed through self-phase modulation (SPM). The GO films are integrated with SOI nanowires using a large-area, transfer-free, layer-by-layer coating method that yields precise control of the film thickness. The film placement and coating length are controlled by opening windows in the silica cladding of the SOI nanowires. Owing to the strong mode overlap between the SOI nanowires and the highly nonlinear GO films, the Kerr nonlinearity of the hybrid waveguides is significantly enhanced. Detailed SPM measurements using picosecond optical pulses show significant spectral broadening enhancement for SOI nanowires coated with 2.2 mm long films of 1–3 layers of GO and 0.4 mm long films with 5–20 layers of GO. By fitting the experimental results with theory, the dependence of GO’s Kerr nonlinearity on layer number and pulse energy is obtained, showing interesting physical insights and trends of the layered GO films from 2D monolayers to quasi bulk-like behavior. Finally, we show that by coating SOI nanowires with GO films, the effective nonlinear parameter of SOI nanowires is increased 16-fold, with the effective nonlinear figure of merit (FOM) increasing by about 20 times to FOM > 5. These results reveal the strong potential of using layered GO films to improve the Kerr nonlinear optical performance of silicon photonic devices.

Graphene oxide films for advanced ultra-flat optical devices and photonic integrated circuits

“…[21]. (e) GO film conformally coated on a silicon nanowire waveguide [79]. (f) Precise GO film patterning on an integrated MRR [54].…”

“…With respect to device fabrication, although the conformal coating of GO films on singlemode silicon nanowire waveguides (with a cross section of 500 nm × 220 nm) has been achieved [79], it is still difficult to achieve conformal coating in structures with feature sizes < 100 nm such as slot waveguides. This is mainly limited by the GO flake size used in solutionbased self-assembly, although this can be reduced via oxidation and vigorous ultrasonics [21].…”

“…SA in GO-coated SOI nanowires[79]. (a) Power-dependent excess insertion loss (EIL) of optical pulses after transmission through the bare and hybrid SOI nanowires.…”

Strongly enhanced four wave mixing in micro-ring resonators integrated with 2D graphene oxide films

“…The measured CE versus Δλ is depicted in Figure 3(d) where we see that, for all three MRRs, the CE only shows a slight decrease with Δλ, reflecting the low dispersion of the doped silica MRR and the GO-coated MRRs, thus enabling effective phase matching for broadband FWM. Compared with other 2D materials, n2 for GO is lower than graphene but still two orders of magnitude higher than bulk silicon [11][12][13][14][15][16], which demonstrates the high potential of GO as a new optical material for nonlinear photonic applications. Further, like Si-Ge heterostructures, [17,18] GO may also offer interesting possibilities for both 2 nd and 3 rd order nonlinear effects courtesy of its complex anisotropic nonlinear optical characteristics.…”

Enhanced 3 rd order optical nonlinearity in silicon nitride nanowires integrated with 2D graphene oxide films

“…The increasing demand for high performing nonlinear integrated photonic devices has motivated the search for highly nonlinear materials [20,29]. The superior Kerr nonlinearity of 2D layered materials such as graphene, graphene oxide (GO), black phosphorus and transition metal dichalcogenides (TMDCs) has been widely recognized and has enabled diverse nonlinear photonic devices with high performance and new functionalities [29][30][31][32][33][34][35][36][37][38][39][40]. In particular, tunable FWM in graphene-covered SiN waveguides has been demonstrated by electronically tuning the Fermi energy of graphene [31].…”